Thermal structure of the low-grade part of Ryoke belt in the Yanai district, Yamaguchi prefecture, southwest Japan

Abstract

The western part of Yamaguchi prefecture is dominated by the unmetamorphosed Kuga group in the north and the low-grade part of Ryoke belt in the south. The Kuga group conformably overlays the Ryoke belt without any structural gaps. According to the degree of graphitization, the metamorphic grade progressively increases from the Kuga group to the Ryoke belt regardless of any deformational features. The Kuga group was formed as the accretionary complex followed by undergoing the low-pressure type of the Ryoke metamorphism. Therefore, the main deformational events occurred to be prior to the Ryoke metamorphism. Therefore, the eastern part of Yamaguchi Prefecture is one of important region to understand the process from accretionary complex to volcanic arc crust.